Conventionally, liquid crystal display devices with built-in touch sensors, i.e., liquid crystal display devices each of which contains a touch sensor have been widely used.
According to the liquid crystal display device with the touch sensor, for example, photo sensors for detecting light is contained in a pixel of a TFT (Thin Film Transistor) liquid crystal display panel included in the liquid crystal display device. When a viewer V of the touch-sensor-provided liquid crystal display device touches the liquid crystal display panel of the touch-sensor-provided liquid crystal display device, an amount of light received by the photo sensors is changed, and the change in the amount of light is used for detecting a position of the touch. The light received by the photo sensors can be, for example, ambient light of the touch-sensor-provided liquid crystal display device or light emitted from a backlight unit provided on a backside of the liquid crystal display panel.
Various configurations have proposed for such a touch-sensor-provided liquid crystal display device.
(Patent Literature 1)
For example, Patent Literature 1 discloses a display device integrated with a touch panel which detects a shadow generated when external light (corresponding to the ambient light) is obstructed by a touch. Patent Literature 1 further discloses a technique for improving accuracy of the detection in which technique the backlight is being turned off during the detection by sensors so that an effect of light emitted from the backlight can be reduced in detecting the shadow.
(Patent Literature 2)
Patent Literature 2 discloses a technique to detect a shadow of an object by photo sensor pixels and then obtain a center position of the shadow, etc., thereby detecting a coordinate position of the object.
Patent Literature 1    Japanese Patent Application Publication, Tokukai, No. 2006-317682 A (Publication Date: Nov. 24, 2006)
Patent Literature 2    Japanese Patent Application Publication, Tokukai, No. 2007-226045 A (Publication Date: Sep. 6, 2007)